Sealed Scroll Compressor for Helium

ABSTRACT

A sealed scroll compressor for helium having a stationary scroll, an orbiting scroll, and an oil-injection mechanism. The oil-injection mechanism has an oil-injection pipe arranged to pass through a sealed container and connected to an oil-injection port, and the opening of the oil-injection port is arranged at a bottom surface of a groove between ridges formed with the scroll wrap of the stationary scroll in such a manner that a first range of the orbital angle of the orbiting scroll is approximately identical to a second range of the orbital angle of the orbiting scroll, where the oil-injection port is connected to the outer compression chamber while the orbital angle of the orbiting scroll is in the first range, and is connected to the inner compression chamber while the orbital angle of the orbiting scroll is in the second range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the foreign priority benefit under 35 U.S.C. §119 of Japanese Patent Application No. 2011-110004, filed on May 17, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sealed scroll compressor for use in refrigeration or air conditioning, and in particular to a sealed scroll compressor for helium.

2. Description of the Related Art

An example of a sealed scroll compressor for helium is disclosed in Japanese Patent Laid-open No. 2009-156234 (hereinafter referred to as JP2009-156234A).

The sealed scroll compressor disclosed in JP2009-156234A has an oil-injection mechanism, in which an oil-injection pipe for cooling the working helium gas is arranged through the wall of a sealed container and is connected to an oil-injection port arranged in an end plate of the stationary scroll. However, the flow rate of the first injected cooling oil into the outer compression chamber on the outer side of the scroll and the flow rate of the second injected cooling oil into the inner compression chamber on the inner side of the scroll are unbalanced, where the outer compression chamber is formed between the outer curved surface of the orbiting scroll (orbital scroll) and the inner curved surface of the stationary scroll, and the inner compression chamber is formed between the inner curved surface of the orbiting scroll and the outer curved surface of the stationary scroll. In other words, the injected cooling oil is not equally distributed to the inner compression chamber and the outer compression chamber in the conventional scroll compressor. FIG. 12 is a graph indicating the relationship between the pressures in the outer compression chamber and the inner compression chamber in a conventional sealed scroll compressor and the sealed scroll compressor according to an embodiment of the present invention (explained later) and the orbital angle of the orbiting scroll. As indicated in the curves indicating variations of the pressures P₁₃ and P₁₄ in the pressure chambers in the conventional sealed scroll compressor in FIG. 12, when the flow rate of the injected cooling oil into the inner compression chamber and the flow rate of the injected cooling oil into the outer compression chamber become unbalanced, the performance in isolating the compression chambers from each other is lowered. Therefore, the rate of the pressure increase (indicated by a compression curve) differs between the compression chambers, and the pressure difference (ΔP_(I)) between the compression chambers increases. The increase in the pressure difference (ΔP_(I)) between the compression chambers can increase the internal leakage. When the internal leakage is increased by the increased pressure difference between the compression chambers, the internal compression power increases, so that the compressor input increases. In addition, since the volume efficiency is lowered during the intake process, the flow rate of helium gas is lowered. Therefore, the performance of the compressor is lowered.

In view of the above, the object of the present invention is to improve the performance of the sealed scroll compressor.

SUMMARY OF THE INVENTION

In order to achieve the above object, according to the first aspect of the present invention, a sealed scroll compressor for helium is provided. The sealed scroll compressor includes: a sealed container; a stationary scroll being contained in the sealed container and having an end plate and a scroll wrap; an oil-injection port having an opening and being arranged in the end plate of the stationary scroll; an oil-injection mechanism having an oil-injection pipe which is arranged to pass through the sealed container and connected to the oil-injection port; and an orbiting scroll contained in the sealed container and interleaved with the stationary scroll to form an outer compression chamber and an inner compression chamber which realize an asymmetric-wrap type compression chambers. The opening of the oil-injection port is arranged at a bottom surface of a groove between ridges formed with the scroll wrap of the stationary scroll in such a manner that a first range of an orbital angle of the orbiting scroll is approximately identical to a second range of the orbital angle of the orbiting scroll, where the oil-injection port is connected to the outer compression chamber while the orbital angle of the orbiting scroll is in the first range, and is connected to the inner compression chamber while the orbital angle of the orbiting scroll is in the second range.

In addition, in order to achieve the aforementioned object, according to the second aspect of the present invention, a sealed scroll compressor for helium is provided. The sealed scroll compressor includes: a sealed container; a stationary scroll being contained in the sealed container and having an end plate and a scroll wrap; an oil-injection port having an opening and being arranged in the end plate of the stationary scroll; an oil-injection mechanism having an oil-injection pipe which is arranged to pass through the sealed container and connected to the oil-injection port; and an orbiting scroll contained in the sealed container and interleaved with the stationary scroll to form an outer compression chamber and an inner compression chamber which realize an asymmetric-wrap type compression chambers. The opening of the oil-injection port is arranged at a bottom surface of a groove between ridges formed with the wrap of the stationary scroll in such a manner that a first range θ₁ of an orbital angle of the orbiting scroll, a second range θ₂ of the orbital angle of the orbiting scroll, a first stroke volume Vth1 in the outer compression chamber, and a second stroke volume Vth2 in the inner compression chamber satisfy a relationship,

θ₁/θ₂≈Vth1/Vth2.

According to the present invention, the performance of the compressor is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of the entire structure of a vertical type sealed scroll compressor for helium according to the embodiment of the present invention;

FIG. 2 is a partial cross-sectional view illustrating part of the sealed scroll compressor of FIG. 1 realizing an oil-injection mechanism;

FIG. 3 is a plane view of a stationary scroll;

FIG. 4 is a vertical cross-sectional view of the stationary scroll;

FIG. 5 is a schematic plane view of an orbiting scroll;

FIG. 6 is a cross sectional view of a configuration in which the stationary and orbiting scroll wraps are assembled together, where the orbiting scroll is at the orbital angle θ_(s1);

FIG. 7 is a cross sectional view of a configuration in which the stationary and orbiting scroll wraps are assembled together, where the orbiting scroll is at the orbital angle θ_(s2);

FIG. 8 is a graph of compression curves in the pressure chambers (i.e., curves indicating variations of the pressures in the pressure chambers with the orbital angle of the orbiting scroll);

FIG. 9 is a partial plane view of a first variation of the stationary scroll, in which the oil-injection port is changed from the stationary scroll 5 of FIG. 3;

FIG. 10 is a graph of compression curves in the pressure chambers (i.e., curves indicating variations of the pressures in the pressure chambers with the orbital angle of the orbiting scroll) in a second variation of the embodiment, in which the oil-injection port is changed from the present embodiment;

FIG. 11 is a plane view of the second variation of the stationary scroll, in which the oil-injection port is displaced from the stationary scroll 5 of FIG. 8; and

FIG. 12 is a graph of compression curves in the pressure chambers (i.e., curves indicating variations of the pressures in the pressure chambers with the orbital angle of the orbiting scroll) in a conventional compressor and a compressor according to the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, the embodiment of the present invention and variations are explained with reference to FIGS. 1 to 12.

First, the structure of the sealed scroll compressor according to the embodiment of the present invention and the flow of working helium gas and the flow of injected cooling oil are explained below with reference to FIGS. 1 and 2. FIG. 1 is a vertical cross-sectional view of the entire structure of the vertical type sealed scroll compressor for helium according to the present embodiment, and FIG. 2 is a partial cross-sectional view illustrating part of the sealed scroll compressor of FIG. 1 realizing an oil-injection mechanism. As illustrated in FIGS. 1 and 2, an oil-injection pipe 31 for injecting (cooling) oil (for use in cooling helium gas) passes through an upper cover 2 a of a sealed container 1 and is connected to an oil-injection port 22, which is arranged in an end plate 5 a of a stationary scroll 5. The opening of the oil-injection port 22 is arranged toward the edge face of a wrap 6 b of an orbiting scroll 6. An intake pipe 17 is arranged on the upper side of the sealed container 1, and a scroll compressor mechanism and a motor unit 3 are respectively held in upper and lower parts in the sealed container 1. The inside of the sealed container 1 is separated by a frame 7 into a discharge chamber 1 a and a motor chamber 1 b.

Compression chambers 8 a and 8 b (which may be collectively referred to as the compression chambers 8) are formed in the scroll compressor mechanism by interleaving the stationary scroll 5 and the orbiting scroll 6 as illustrated in FIGS. 6 and 7. The stationary scroll 5 is constituted by the end plate 5 a and a wrap 5 b, where the end plate 5 a has a round platelike shape, and the wrap 5 b is arranged perpendicular to the end plate 5 a and formed to have the shape of an involute (or a curve near to an involute) in every cross section parallel to the end plate 5 a. In addition, a discharge port 10 is arranged in the center of the stationary scroll 5, and an intake port 15 is arranged in a peripheral part of the stationary scroll 5. The orbiting scroll 6 is constituted by an end plate 6 a, the wrap 6 b, and a boss 6 c. The end plate 6 a has a round platelike shape. The wrap 6 b is arranged perpendicular to the end plate 6 a and formed to have a shape similar to the wrap 5 b of the stationary scroll 5. The boss 6 c is formed on the side, opposite to the wrap 6 b, of the end plate 6 a. A main bearing 40 is formed in the center of the frame 7, and a rotating shaft 14 is supported by the main bearing 40. An eccentric shaft 14 a, which is formed at the tip of the rotating shaft 14, is pivotally inserted into the boss 6 c. The stationary scroll 5 is fixed to the frame 7 with multiple bolts. In addition, the orbiting scroll 6 is supported by the frame 7 through an Oldham mechanism 38 (which is constituted by an Oldham ring and Oldham keys) in such a manner that the orbiting scroll 6 orbits with respect to the stationary scroll 5 without being rotated.

A motor shaft 14 b is integrally coupled to the rotating shaft 14, and is directly connected to the motor unit 3. The intake pipe 17 passes through the upper cover 2 a of the sealed container 1, and is connected to the intake port 15 of the stationary scroll 5.

The discharge chamber 1 a has the discharge port 10 as an opening, so that the discharge chamber 1 a is connected to the motor chamber 1 b through first paths 18 a and 18 b, which are arranged in peripheral regions of the frame 7. The motor chamber 1 b is connected to a discharge pipe 20, which passes through a casing 2 b. The casing 2 b constitutes the central part of the sealed container 1. The discharge pipe 20 is located on the side of the sealed container 1 nearly opposite to the first paths 18 a and 18 b. The motor chamber 1 b is separated by a (motor) stator 3 a into an upper space 1 b 1 and a lower space 1 b 2. In addition, in order to allow the oil and gas to flow between the upper space 1 b 1 and the lower space 1 b 2, the upper space 1 b 1 and the lower space 1 b 2 are connected through paths 25 b and 25 c (which may be collectively referred to as the paths 25). The paths 25 b and 25 c are formed in the gaps between the motor stator 3 a and the inner wall surface 2 m of the casing 2 b.

Further, the upper space 1 b 1 and the lower space 1 b 2 are also connected through the motor air gap 26. Since a mixture of the gas and the cooling oil flows in the motor chamber 1 b through the above paths, the motor can be directly cooled with the injected oil, the temperature of which is relatively low (e.g., 60° C. to 70° C.).

An O-ring 53 is arranged between the intake pipe 17 and the stationary scroll 5 for hermetically separating the high-pressure region and the low-pressure region. In addition, a back-pressure chamber 36 is realized by the space located on the rear side of the end plate of the orbiting scroll 6. That is, the back-pressure chamber 36 is a space enclosed by the scroll compressor mechanism and the frame 7. An intermediate pressure between the intake pressure P_(s) and the discharge pressure P_(d) is introduced into the back-pressure chamber 36 through a pore 6 d perforated through the end plate of the orbiting scroll 6, so that the intermediate pressure exerts force in the axial direction to the orbiting scroll 6, and presses the orbiting scroll 6 to the stationary scroll 5.

Lubricating oil 23 is reserved at the bottom of the sealed container 1. The lubricating oil 23 is sucked into an oil-suction tube 27 by the centrifugal pump effect which is produced by an eccentric cavity 13 arranged in the rotating shaft 14, flows in the rotating shaft 14, and is then supplied to a scroll bearing 32. The oil supplied to the scroll bearing 32 and discharged from the scroll bearing 32 drops to the main bearing 40 (which is a roller bearing), moves to the bottom end of the frame, is lead through a discharge tube 74, and returns to an oil reservoir in a bottom chamber 2 c. In addition, the oil supplied to the scroll bearing 32 and discharged from the scroll bearing 32 moves to the back-pressure chamber 36 through a sealing means 85 which has a ring-shaped sealing structure.

As illustrated in FIG. 2, pocket pores 58 are arranged on the end face (facing the sealing means 85) of the boss 6 c of the orbiting scroll 6, so that the oil in the pocket pores 58 is intermittently discharged to the back-pressure chamber 36 by the orbiting motion of the orbiting scroll 6. Then, the oil moved to the back-pressure chamber 36 is injected through the aforementioned pore 6 d into only the outer compression chamber 8 a (which is fanned on the outer side of the wrap 6 b of the orbiting scroll 6), is mixed with compressed gas in the outer compression chamber 8 a, and is thereafter discharged to the discharge chamber 1 a together with the helium gas.

In order to drain the lubricating oil 23 accumulated at the bottom of the sealed container 1, an injected-oil outlet part 29 is arranged through the bottom of the sealed container 1, and an oil-drain pipe 30 is connected to the injected-oil outlet part 29. The lubricating oil 23 accumulated at the bottom of the sealed container 1 flows into the inflow part 30 a of the outlet part 29 and flows through the oil-drain pipe 30 due to the difference between the discharge pressure P_(d) in the sealed container 1 and the internal pressures P_(i1) and P_(i2) (which may be collectively referred to as P_(i)) of the compression chambers 8. Further, a bore reduction means 30 m is arranged in the path 30 f inside the injected-oil outlet part 29, where the bore reduction means 30 m has a diameter equivalent to the diameter of a bore reduction means 31 m which is arranged in oil-injection piping.

Although the arrangement around the oil-injection pipe 31 are explained in detail later, the bore reduction means 31 m is arranged in a path 31 f which is located inside the oil-injection pipe 31 immediately in front of the oil-injection port 22 of the oil-injection pipe 31, where the diameter of the bore reduction means 31 m is smaller than the diameter d₀ of the oil-injection port 22.

FIG. 3 is a plane view of the stationary scroll 5, FIG. 4 is a vertical cross-sectional view of the stationary scroll 5, and FIG. 5 is a schematic plane view of the orbiting scroll 6. As illustrated in FIGS. 3 to 5 and as mentioned before, the stationary scroll 5 is constituted by the end plate 5 a and a wrap 5 b, where the end plate 5 a has a round platelike shape, and the wrap 5 b is arranged perpendicular to the end plate 5 a and formed to have the shape of an involute (or a curve near to an involute) in every cross section parallel to the end plate 5 a. In addition, a discharge port 10 is arranged in the center of the stationary scroll 5, and an intake port 15 (constituted by a first part 15 a connected to the intake pipe 17 and a second part 15 b connected to the first part 15 a) is arranged in a peripheral part of the stationary scroll 5.

In the plane view illustrated in FIG. 3, O_(k) denotes the center of the coordinates, and X_(k) and X_(k) are coordinate axes. The point 64 is the outermost point of contact corresponding to the position at which the end of the wrap 6 b comes in contact with the inner surface 561 of the stationary scroll 5 when the outer compression chamber 8 a is formed (as illustrated in FIG. 6), and the point 63 is the outermost point of contact corresponding to the position at which the end of the wrap 6 b comes in contact with the outer surface 562 of the stationary scroll 5 when the inner compression chamber 8 b is formed (as illustrated in FIG. 7). That is, the outer compression chamber 8 a is formed between the outer surface 661 of the orbiting scroll 6 and the inner surface 561 of the stationary scroll 5, and the inner compression chamber 8 b is formed between the inner surface 662 of the orbiting scroll 6 and the outer surface 562 of the stationary scroll 5. In the plane view of FIG. 3, the point 64 (indicating the outermost position of contact with the end of the wrap 6 b when the outer compression chamber 8 a is formed) is the end of a scroll wrap curve which is extended from the end point 63 of the scroll wrap curve of the outer surface 562 of the stationary scroll 5 by at most π rad, where it is the circle ratio (i.e., the ratio of the circumference to the diameter of a circle). The above scroll wrap curve realizes asymmetric-wrap type compression chambers. For example, in the arrangement illustrated in FIG. 7, the meaning of the “asymmetric-wrap type” is that the pressures in the outer and inner compression chambers 8 a and 8 b (which have crescent-like cross sections) are different, i.e., the compression chambers 8 a and 8 b are asymmetric with respect to the pressure, although the volumes of the compression chambers 8 a and 8 b (and the cross sections of the compression chambers 8 a and 8 b) are identical. Such a scroll compressor is called a asymmetric-wrap type compressor. The angle at which the scroll wrap ends may be indicated by the involute scroll angle.

In order to cool the body of the compressor and lower the temperature of the helium gas which is heated by adiabatic compression, the sealed scroll compressor according to the present invention has the structure for injection of oil for cooling. In the structure, the oil-injection port 22 is a single port, and is slightly displaced outward, in the plane view parallel to the end plate 5 a, from the center of a groove between ridges formed with the wrap 5 b as illustrated in FIGS. 3 and 4. The opening diameter d₀ of the oil-injection port 22 is set to satisfy d₀>t, where t is the thickness of the scroll wrap 6 b. Thus, it is possible to avoid covering of the oil-injection port 22 by the thickness of the teeth (i.e., the edge of the scroll wrap 6 b).

As illustrated in FIG. 4, a round bore 22 a for insertion of the path 31 m is arranged immediately in front of the oil-injection port 22 in the stationary scroll 5. The oil-injection port 22 is arranged to have an opening at the bottom surface 5 m of the groove between the ridges formed with the wrap 5 b, and the center 22 f of the opening of the oil-injection port 22 is located at a position displaced from the end 63 or 64 of the scroll wrap 6 b toward the inner end (at the origin O_(k)) of the wrap 5 b along the scroll of the wrap 5 b by the scroll wrap angle Δλ₀ of approximately 1.5 π rad, where it is the circle ratio. The stroke volume Vth1 of the outer compression chamber 8 a and the stroke volume Vth2 of the inner compression chamber 8 b satisfy the relationship Vth1>Vth2, and the ratio Vth1/Vth2 is approximately 1.1 to 1.2. Therefore, control of the flow rates of the cooling oil injected into the outer and inner compression chambers 8 a and 8 b according to the flow rates Vth1 and Vth2 of intake gas is effective in cooling.

In order to achieve the above effect, the center 22 f of the oil-injection port 22 is slightly displaced outward (i.e., toward the inner surface 561 of the stationary scroll 5) from the center of the groove between the ridges formed with the wrap 5 b, as illustrated in the plane view of FIG. 3 or the vertical cross-sectional view of FIG. 4. Specifically, the ratio S₂/D_(t) of the distance S2 between the inner surface 561 of the stationary scroll 5 and the center 22 f of the oil-injection port 22 to the width D_(t) of the groove between the ridges formed with the wrap 5 b is approximately 0.45 to 0.48 in this example.

In the plane view of FIG. 5, the wrap 6 h in the orbiting scroll 6 is formed to realize the outer surface 661 of which ends with an outer end portion 6 k. The points 82 a and 83 a are at the scroll wrap angle at which the scroll wrap 6 b ends. As illustrated in the plane view of FIG. 5, the points 82 a and 83 a in the outer end portion 6 k of the wrap 6 b are smoothly connected through an arc having a radius R₄ in every cross section parallel to the end plate 6 a. That is the outer surface 661 of the orbiting scroll 6 and the inner surface 662 of the orbiting scroll 6 are continuously connected at the outer end portion 6 k with the arc radius R₄. Similarly, the outer surface 661 of the orbiting scroll 6 and the inner surface 662 of the orbiting scroll 6 are continuously connected at an inner end portion 6 n with an arc radius R₅. In addition, the aforementioned single pore 6 d, which passes through the end plate 6 a, is singly arranged at a position along the outer surface 661 of the orbiting scroll 6.

FIG. 6 is a cross sectional view of a state, at completion of a process of intake into the outer compression chamber 8 a, of a configuration in which the stationary scroll 5 and the orbiting scroll 6 are assembled. In the state of FIG. 6, the orbiting scroll 6 is at the angular position of the orbital angle θ_(s1), at which the opening of the oil-injection port 22 is connected to only the outer compression chamber 8 a.

FIG. 7 is a cross sectional view of a state, at completion of a process of intake into the inner compression chamber 8 b, of the configuration in which the stationary scroll 5 and the orbiting scroll 6 are assembled. In the state of FIG. 7, the orbiting scroll 6 is at the angular position of the orbital angle θ_(s2), at which the opening of the oil-injection port 22 is connected to only the inner compression chamber 8 b.

FIG. 8 is a graph of compression curves in the pressure chambers (i.e., curves indicating variations of the pressures in the pressure chambers with the orbital angle of the orbiting scroll 6). FIG. 8 indicates variations in the pressure P_(i1) in the outer compression chamber 8 a and the pressure P_(i2) in the inner compression chamber 8 b while the orbital angle varies π rad. The angular position of the orbital angle θ_(s1) is the position at which compression of the outer compression chamber 8 a starts, and the angular position of the orbital angle θ_(s2) is the position at which compression of the inner compression chamber 8 b starts.

As mentioned before, the opening of the oil-injection port 22 is arranged at the bottom surface 5 m of the groove between the ridges formed with the wrap 5 b in the stationary scroll 5. In this case, the range (width) θ₁ of the orbital angle in which the outer compression chamber 8 a is connected to the oil-injection port 22 and the range (width) θ₂ of the orbital angle in which the inner compression chamber 8 b is connected to the oil-injection port 22 can be set to make the ratio θ₁/θ₂ as great as (nearly equal to) the ratio V₀=Vth1/Vth2. In the example of FIG. 3, the ratio θ₁/θ₂ is approximately 1.1 to 1.2.

FIG. 8 indicates that the operation of injecting the oil is started at the angle which is θ₅ before the orbital angle θ_(s1), where the process of intake into the outer compression chamber 8 a is completed at the orbital angle θ_(s1). In this case, the intake chamber 5 f formed outside the wrap 5 b is connected to the oil-injection port 22 while the orbital angle of the orbiting scroll 6 is in the range θ₅. That is, the intake chamber 5 f formed outside the wrap 5 b is intermittently connected to the oil-injection port 22, so that the helium gas in the intake chamber 5 f is cooled. In addition, while the orbital angle of the orbiting scroll 6 is in the range θ₆, both of the outer and inner compression chambers 8 a and 8 b are concurrently connected to the oil-injection port 22 (or to the port 228 in the first variation illustrated in FIG. 9). The range θ₅, in which the intake chamber 5 f is connected to the oil-injection port 22, is adjusted by arranging the opening of the oil-injection port 22 at the groove bottom between the ridges of the wrap 5 b in such a manner that the center of the opening of the oil-injection port 22 is displaced outward from the center of the width of the groove bottom.

FIG. 9 is a plane view of a first variation of the stationary scroll in the sealed scroll compressor according to the embodiment. The first variation of the embodiment is different from the stationary scroll 5 illustrated in FIG. 3 in the shape of the opening 228 of the oil-injection port, and the opening 228 of the oil-injection port is elongated in the radial direction. Practically, the dimension L₇ of the opening 228 in the radial direction is approximately 2.5 times the thickness t of the wrap 5 b, and the dimension L₈ of the opening 228 in the circumferential direction is set at most equivalent to the thickness t of the wrap 5 b. The range (width) θ₁ of the orbital angle in which the outer compression chamber 8 a is connected to the oil-injection port 228 can be set by adjusting the dimension L₇ of the opening 228 in the radial direction. Further, both of the outer and inner compression chambers 8 a and 8 b can be concurrently connected to the oil-injection port 22 in the case where the opening diameter d₀ of the oil-injection port 22 is set to satisfy d₀>t, and both of the outer and inner compression chambers 8 a and 8 b can be concurrently connected to the oil-injection port 228 in the case where the dimension L₇ of the opening 228 in the radial direction is set to satisfy L₇>t.

Since the means for equally distributing the injected oil according to the present embodiment can relatively reduce the variations in the pressure difference in oil injection (i.e., the differences between the discharge pressure P_(d) and the pressures P_(i1) and P_(i2) in the outer and inner compression chambers 8 a and 8 b) and reduce the oil hammer effect which is caused when the oil is injected. Therefore, it is possible to reduce vibration in the oil injection piping and the piping stress. Further, it is possible to suppress the flow sound (pulsating sound) inside the oil-injection piping, and therefore reduce the noise and vibration of the compressor.

FIG. 11 is a plane view of a second variation of the stationary scroll in the sealed scroll compressor according to the present embodiment. As illustrated in FIG. 11, the second variation of the embodiment is different from the first variation in that the opening 222 of the oil-injection port in the second variation (illustrated in FIG. 11) is located at a position displaced from the position of the opening 228 of the oil-injection port in the first variation (illustrated in FIG. 9) toward the inner end (at the origin O_(k)) of the wrap 5 b along the scroll of the wrap 5 b by the scroll wrap angle of approximately 0.5 π rad, where π is the circle ratio. Similarly to the first variation, the opening 222 of the oil-injection port is elongated in the radial direction.

FIG. 10 is a graph of compression curves in the outer and inner compression chambers 8 a and 8 b (i.e., curves indicating variations of the pressures in the outer and inner compression chambers 8 a and 8 b with the orbital angle of the orbiting scroll 6) in the second variation. In FIG. 10, the range (width) θ₃ of the orbital angle in which the outer compression chamber 8 a is connected to the oil-injection port 222 and the range (width) θ₄ of the orbital angle in which the inner compression chamber 8 b is connected to the oil-injection port 222 are almost equalized (i.e., θ₃≈θ₄). Practically, each of the ranges θ₃ and θ₄ has a width of approximately 200 to 230 degrees. In addition, while the orbital angle of the orbiting scroll 6 is in the range θ₇, both of the outer and inner compression chambers 8 a and 8 b are concurrently connected to the oil-injection port 222.

The sealed scroll compressors according to the present embodiment and the first and second variations are characterized in that the center of the opening of the oil-injection port 22, 228, or 222 is located at a position displaced from the end 63 or 64 of the scroll wrap 5 b toward the inner end (at the origin O_(k)) of the wrap 5 b along the scroll of the wrap 5 b by the scroll wrap angle Δλ₀ of approximately 1.5 π to 2 π rad, where π is the circle ratio.

In the sealed scroll compressors according to the present embodiment and the first and second variations, the oil flowing into the oil-drain pipe 30 passes through external oil piping 51 and is then inputted into an oil cooler 33. After the oil is cooled in the oil cooler 33, the cooled oil passes through the oil-injection pipe 31 and the oil-injection port 22 (or 228 or 222) and is injected into the outer and inner compression chambers 8 a and 8 b. As illustrated in FIG. 2, an O-ring 48 is arranged around the bore reduction means 31 m for hermetically isolating the pressure in the oil-injection pipe 31 from the high pressure in the discharge chamber 1 a.

The structures and mechanisms explained above enables equal distribution of the injected cooling oil into the outer and inner compression chambers, and achieves uniformity in the cooling performance. As indicated in the curves indicating variations of the pressures P_(i1) and P_(i2) in the pressure chambers in the embodiment and the curves indicating variations of the pressures P_(i3) and P_(i4) in the pressure chambers in the conventional sealed scroll compressor, the oil-injection function which equally distributes the injected oil to the outer and inner compression chambers 8 a and 8 b enhances the effect of the cooling oil in isolating the outer and inner compression chambers from each other, so that the rates of the pressure increase (indicated by the compression curves) in the present embodiment is lower than the conventional sealed scroll compressor. Therefore, for example, the pressure difference (ΔP₂) between the adjacent compression chambers in the present embodiment is smaller than the pressure difference (ΔP₁) between the adjacent compression chambers in the conventional sealed scroll compressor. The decrease in the pressure difference between the adjacent compression chambers reduces the internal leakage and the compression power, and increases the volume efficiency. Thus, the performance and the efficiency of the compressor are greatly improved. In addition, the cooling oil equally distributed to the outer and inner compression chambers 8 a and 8 b enhances the effects of cooling and isolating the working gas in the outer and inner compression chambers 8 a and 8 b, and achieves thorough and effective lubrication of the sliding parts such as the edges of the scroll wraps. Further, since the compression power is reduced, the loads acting on the sliding parts such as the bearings are also reduced, so that the reliability of the compressor increases. Furthermore, the decrease in the bearing loads increases the lifetimes of the antifriction bearings such as the main bearing 40 and the scroll bearing 64. 

1. A sealed scroll compressor for helium, comprising: a sealed container; a stationary scroll being contained in the sealed container and having an end plate and a scroll wrap; an oil-injection port having an opening and being arranged in the end plate of the stationary scroll; an oil-injection mechanism having an oil-injection pipe which is arranged to pass through the sealed container and connected to the oil-injection port; and an orbiting scroll contained in the sealed container and interleaved with the stationary scroll to form an outer compression chamber and an inner compression chamber which realize an asymmetric-wrap type compression chambers; wherein the opening of the oil-injection port is arranged at a bottom surface of a groove between ridges formed with the scroll wrap of the stationary scroll in such a manner that a first range of an orbital angle of the orbiting scroll is approximately identical to a second range of the orbital angle of the orbiting scroll, and the oil-injection port is connected to the outer compression chamber while the orbital angle of the orbiting scroll is in the first range, and is connected to the inner compression chamber while the orbital angle of the orbiting scroll is in the second range.
 2. The sealed scroll compressor according to claim 1, wherein a center of the opening is displaced outward from a center of the bottom surface.
 3. The sealed scroll compressor according to claim 1, wherein the opening has a shape elongated in a radial direction of the stationary scroll.
 4. The sealed scroll compressor according to claim 1, wherein each of the first range and the second range has a width of approximately 200 to 230 degrees.
 5. The sealed scroll compressor according to claim 1, wherein a center of the opening is located at a position displaced from an end of the scroll wrap of the stationary scroll toward an inner end of the scroll wrap of the stationary scroll along the scroll wrap of the stationary scroll by a scroll wrap angle of approximately 1.5 π to 2 π rad, where it is the circle ratio.
 6. A sealed scroll compressor for helium, comprising: a sealed container; a stationary scroll being contained in the sealed container and having an end plate and a scroll wrap; an oil-injection port having an opening and being arranged in the end plate of the stationary scroll; an oil-injection mechanism having an oil-injection pipe which is arranged to pass through the sealed container and connected to the oil-injection port; and an orbiting scroll contained in the sealed container and interleaved with the stationary scroll to form an outer compression chamber and an inner compression chamber which realize an asymmetric-wrap type compression chambers; wherein the opening of the oil-injection port is arranged at a bottom surface of a groove between ridges formed with the wrap of the stationary scroll in such a manner that a first range θ₁ of an orbital angle of the orbiting scroll, a second range θ₂ of the orbital angle of the orbiting scroll, a first stroke volume Vth1 in the outer compression chamber, and a second stroke volume Vth2 in the inner compression chamber satisfy a relationship, θ₁/θ₂≈Vth1/Vth2.
 7. The sealed scroll compressor according to claim 6, wherein a center of the opening is displaced outward from a center of the bottom surface.
 8. The sealed scroll compressor according to claim 6, wherein the opening has a shape elongated in a radial direction of the stationary scroll.
 9. The sealed scroll compressor according to claim 6, wherein a center of the opening is located at a position displaced from an end of the scroll wrap of the stationary scroll toward an inner end of the scroll wrap of the stationary scroll along the scroll wrap of the stationary scroll by a scroll wrap angle of approximately 1.5 π to 2 π rad, where n is the circle ratio. 